488 PHANEROGAMS. 



bipartition, the pollen-cells are produced from their mother-cells in a similar manner. 

 Moreover, in the points here indicated Gymnosperms' again appear as a connecting 

 link between Cryptogams and Angiosperms ; the pollen-sacs of Cycadeae and of 

 some Coniferse closely resembling, in form and position, the sporangia of some 

 Vascular Cryptogams. 



The general result of these observations is that the Phanerogam, with its 

 pollen-grains and its embryo-sacs, is equivalent to the spore-producing (asexual) 

 generation (Sporophore) of the Vascular Cryptogams. But as in Vascular Cryp- 

 togams the sexual differentiation first makes its appearance (in Ferns and Equise- 

 taceas) in the prothallium only, and next (in Rhizocarpese and Ligulatge) in the 

 spores themselves, so, in Phanerogams, this process is carried back a step further, 

 the sexual differentiation arises still earlier, being manifested not only in the forma- 

 tion of embryo-sac and pollen-grains, but also in the difference between ovule and 

 pollen-sac, and between the leaves bearing them (carpels and stamens), and even 

 earlier in the distinction between male and female flowers, and last of all in the 

 dioecious condition of the plants themselves^. [The sexual generation (Oophore) 

 is represented in the pollen-grains (microspores) by the formation of cells within 

 them which correspond to a male prothallium, and in the embryo-sac (macrospore) 

 by the formation of the egg-apparatus, antipodal cells, and endosperm, which together 

 correspond to a female prothallium. A distinct alternation of generations can there- 

 fore be traced in the life-history of a Phanerogam.] 



The fertilised oosphere of Phanerogams produces a Suspensor, growing towards 

 the base of the embryo-sac and dividing, a structure which we have already met with 

 in Selaginella, on the apex of which there is a mass of tissue at first almost globular, 

 which is the embryo. The development of the embryo usually proceeds, even 

 before the maturity of the seed, to such an extent that the first leaves, the primary 

 axis, and the first root, can be clearly distinguished. It is only in parasites and 

 saprophytes devoid of chlorophyll that the embryo usually remains rudimentary until 

 the dissemination of the seeds without discernible external differentiation; while 

 in those Phanerogams which contain chlorophyll the embryo not unfrequently 

 attains a very considerable size and external differentiation (as in Pinus, Zea, 

 ^sculus, Quercus, Fagus, Phaseolus, &c.) Independendy of any curving of the 

 embryo, the primary apex of its stem always lies originally pointing towards the 

 bottom of the embryo-sac (the base, chalaza^ of the ovule) ; the first root (primary 

 root) coincides with a posterior prolongation of the primary stem ; it faces the apex 

 (micropylar end) of the embryo-sac, and is of distinctly endogenous origin, inasmuch 

 as its first rudiment at the posterior end of the embryo is covered by the nearest 

 cells of the suspensor. 



The apical cell of the punctum vegetatiom's, which is easily recognised in many Algae, 

 in Characese, Muscineae, Ferns, Equisetaceae, and Rhizocarpeae, as the primary mother- 

 cell of the tissue, has already, as we have seen, been replaced by a small-celled 

 primary meristem in the Lycopodiacese. The apical growth of the axes, leaves, and 

 roots of Phanerogams also can no longer be referred to the activity of a single apical 

 cell from which the whole primary meristem has proceeded. Even in those cases 



^ Compare what is said on Dichogamy in Book III. 



